In reciprocating machinery, and particularly rock breakers, there is a requirement to dampen the motion of the reciprocating machanism on the recoil stroke. In some rock breakers an eccentric mechanism provides intermittent power strokes to the rock breaker tip or shank through an intermediate impact link located between the eccentric and the shank. In the earlier impact devices the shank was usually impacted directly by the eccentric ring. A seal was generally provided between the shank and the housing. The seal generally experienced a short life due to the large number of cycles and large displacement (81/2 to 9 cm) during each cycle. Recoil of the shank was absorbed by conventional dampening devices located exterior of the drive mechanism. An example of such an exterior recoil damper is found in U.S. Pat. No. 3,868,145.
With the advent of a limited displacement (11/2 cm) type intermediate impact link positioned between the eccentric and the shank, the intermediate impact link itself must be dampened as it is relatively free floating in comparison to the more conventional shank and eccentric. That is, the intermediate impact link, being located between the enclosed eccentric and the exterior shank, transmits the force of the eccentric to the shank. In order to provide relatively free movement toward the shank, the intermediate impact link is mounted in appropriate bearings positioned in the housing. However, upon recoil, the recoil force would ordinarily be transmitted to the eccentric thus causing excessive wear on the eccentric unless some form of recoil damper is used.
In such intermediate impact link type rock breakers, the force to be applied to the shank ordinarily does not occur until the shank is displaced rearwardly to engage the intermediate impact link which is also displaced rearwardly into position to be contacted by the eccentric. As the eccentric rotates so that its periphery contacts the intermediate impact link, the force of the eccentric is transmitted through the intermediate impact link to the shank which in turn acts on the working surface. As the eccentric continues to rotate, the force is relieved from the intermediate impact link, thus permitting the shank to recoil with such recoil transmitted to the intermediate impact link. Although the motion of the shank could be dampened in the manner shown in U.S. Pat. No. 3,868,145, that is an exterior damper may be mounted adjacent the shank, the recoil motion of the intermediate impact link which is contained substantially within the housing must also be dampened.
The present invention is directed to overcoming one or more of the problems as set forth above.